Physiological stress responses of the freshwater chondrostean paddlefish ( Polyodon spathula) to acute physical disturbances

Abstract

Juvenile paddlefish ( Polyodon spathula) subjected to various physical disturbances showed significant increases in plasma cortisol and lactate, but little or no change in plasma glucose, chloride or hematocrit. When paddlefish were given a 30 s aerial emersion handling stressor, plasma cortisol increased from 2.2±0.6 to 11±1.8 ng ml −1 in 1 h but had returned to the prestress level by 3 h. Addition of 0.5% NaCl to the recovery tanks had no effect on plasma cortisol changes. Plasma lactate rose from 26±2.6 to 52±4.5 mg dl −1 within 3 h. Plasma cortisol increased to 14±4.8 ng ml −1 and plasma lactate rose to 67±3.7 mg dl −1 after fish were continuously chased in their home tanks for 1 h; plasma lactate remained elevated for 5 h. In fish severely confined for 6 h in cages with intermittent handling, plasma cortisol rose from 6.2±1.6 ng ml −1 to its peak level of 74±6.3 ng ml −1 by 2 h, but approached the prestress value after 18 h of recovery. Plasma lactate levels in confined fish increased from 27±2.7 to 73±6.9 mg dl −1 by 3 h but had returned to near-resting levels by 24 h. The results suggest that paddlefish do not exhibit physiological stress responses to physical disturbances similar in magnitude to those previously documented for many teleostean fishes including salmonids, although cortisol was determined to be the principle steroid released during stress.